Wind turbine rotor blades are well known. A known wind turbine rotor blade is disclosed in EP 1 845 258 A1 containing a cylindrical root portion, an airfoil portion and a transition portion between the root portion and the airfoil portion with a shoulder as border line between the transition portion and the airfoil portion which ends at the tip of the rotor blade.
The geometry of the airfoil portion of the rotor blade between the shoulder and the tip may have a varying chord with a rather linear, concave or convex chord distribution. The linear chord distribution is easy to manufacture but reveals disadvantages in the overall annual energy production rate. The convex chord distribution of the airfoil portion is basically optimized with respect to structural specifications and reveals a high mechanical stress resistance and durability. The concave chord distribution of the rotor blade is usually optimized with respect to the annual energy production. Therefore the selected chord distribution of the rotor blade is usually a compromise between the energy production rate and durability or cost of the rotor blade.
The prior art document WO 2007/045244 A1 discloses a rotor blade with a root portion and a chord or airfoil portion and a transition portion between the root portion and the airfoil portion. The root portion is split into two partitions and an air gap is formed between the two partitions of the root portion. This reduces the mechanical strength and increases the manufacturing costs since the root portion is difficult to produce.
The prior art document EP 1 295 032 A1 discloses a rotor blade of a wind turbine which contains ribs or members which are used as vortex generators.
Nevertheless the inboard portion and the cylindrical root portion of the rotor blade does not contribute to the annual energy production and therefore this portion is less relevant for the performance of energy production of the rotor blade.
On the other hand the inboard portion including the root portion of the blade is necessary for the structural integrity of the rotor blade and for fastening the rotor blade at the wind turbine rotor.